Power density and component costs are key performance metrics of both isolated and non-isolated DC-DC power converters to provide the smallest possible physical size and/or lowest costs for a given output power requirement or specification. Resonant power converters are particularly useful for high switching frequencies such as frequencies above 1 MHz where switching losses of standard SMPS topologies (Buck, Boost etc.) tend to be unacceptable for conversion efficiency reasons. High switching frequencies are generally desirable because of the resulting decrease of the electrical and physical size of circuit components of the power converter like inductors and capacitors. The smaller components allow increase of the power density of the DC-DC power converter. In a resonant power converter an input “chopper” semiconductor switch (often MOSFET or IGBT) of the standard SMPS is replaced with a “resonant” semiconductor switch. The resonant semiconductor switch relies on resonances of circuit capacitances and inductances to shape the waveform of either the current or the voltage across the semiconductor switch such that, when state switching occurs in the semiconductor switch, there is essentially no current through or essentially no voltage across the semiconductor switch. Hence power dissipation is largely eliminated in at least some of the intrinsic capacitances or inductances of the input semiconductor switch such that a marked increase of the switching frequency becomes feasible for example to values above 10 MHz. This concept is known in the art under designations like zero voltage and/or zero current switching (ZVS and/or ZCS) operation. Commonly used switched mode power converters operating under ZVS and/or ZCS are often described as class E, class F or class DE inverters or power converters.
In view of the above, it remains a challenge to reduce the size and lower the component costs of both isolated and non-isolated DC-DC power converters. Hence, novel resonant step-down DC-DC power converter topologies which reduce the required maximum voltage or power rating of active and passive components of the resonant DC-DC converter are highly desirable. Likewise, novel resonant step-down DC-DC power converter topologies which reduce the physical size or cost of active and passive components for example inductors, capacitors, transistors and diodes are highly desirable.